Research Article Vol. 27, No. 16 / 5 August 2019 / Optics Express 23067 High index contrast photonic platforms for on-chip Raman spectroscopy A LI R AZA , 1,2,* S TÉPHANE C LEMMEN , 1,2,3 P IETER WUYTENS , 1,2 MICHIEL DE G OEDE , 4 A MY S. K. TONG , 5 N ICOLAS L E T HOMAS , 1,2 C HENGYU L IU, 6 J IN S UNTIVICH , 7,8 A NDRE G. S KIRTACH , 2,9 S ONIA M. G ARCIA -B LANCO, 4 DANIEL J. B LUMENTHAL , 10 J AMES S. WILKINSON , 5 AND ROEL BAETS 1,2 1 Photonics Research Group, INTEC Department, Ghent University-imec, Technologiepark-Zwijnaarde, 9052 Ghent, Belgium 2 Center for Nano- and Biophotonics, Ghent University, Belgium 3 Laboratoire d’information quantique, Université Libre de Bruxelles, 1050 Bruxelles, Belgium 4 Optical Sciences Group, MESA + Institute of Nanotechnology, University of Twente, 4617, The Netherlands 5 Optoelectronics Research Centre (ORC), University of Southampton, Highfield, Southampton, SO17 1BJ, UK 6 School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA 7 Materials Science and Engineering Department, Cornell University, Ithaca, NY 14853, USA 8 Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY 14853, USA 9 Department of Biotechnology, Ghent University, Ghent, Belgium 10 Optical Communications and Photonic Integration Group (OCPI), UC Santa Barbara (UCSB), Santa Barbara, CA 93106, USA * ali.raza@ugent.be Abstract: Nanophotonic waveguide enhanced Raman spectroscopy (NWERS) is a sensing technique that uses a highly confined waveguide mode to excite and collect the Raman scattered signal from molecules in close vicinity of the waveguide. The most important parameters defining the figure of merit of an NWERS sensor include its ability to collect the Raman signal from an analyte, i.e. “the Raman conversion efficiency” and the amount of “Raman background” generated from the guiding material. Here, we compare different photonic integrated circuit (PIC) platforms capable of on-chip Raman sensing in terms of the aforementioned parameters. Among the four photonic platforms under study, tantalum oxide and silicon nitride waveguides exhibit high signal collection efficiency and low Raman background. In contrast, the performance of titania and alumina waveguides suffers from a strong Raman background and a weak signal collection efficiency, respectively. © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement 1. Introduction High index contrast (HIC) waveguide structures allow a guided pump beam to interact efficiently with an analyte present in its vicinity. The analyte is excited using the waveguide mode and the scattered signal couples back to the same waveguide. This waveguide based excitation and collection technique can be used for different sensing phenomena, e.g. on-chip fluorescence [1], spontaneous Raman [2], stimulated Raman [3] and surface enhanced Raman spectroscopy [4], whereby unlike confocal approaches, the signal scales with the waveguide length. Different photonic structures i.e. optical fibers [5,6], planar waveguides [7], strip waveguides [8–12] and more recently slot waveguides [13] have been successfully used for this purpose. HIC waveguides of few millimeters length also provide the ease of use where an analyte can simply be drop casted unlike hollow core fibers [14]. An integrated photonic waveguide can, therefore, constitute the #368114 https://doi.org/10.1364/OE.27.023067 Journal © 2019 Received 28 May 2019; accepted 21 Jun 2019; published 29 Jul 2019